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Öğe ASCT2 (SLC1A5)-Deficient Mice Have Normal B-cells Developments, proliferation, and Antibody Production(Frontiers Media Sa, 2017) Masle-Farquhar, Etienne; Broer, Angelika; Yabas, Mehmet; Enders, Anselm; Broer, StefanSLC1A5 (solute carrier family 1, member 5) is a small neutral amino acid exchanger that is upregulated in rapidly proliferating lymphocytes but also in many primary human cancers. Furthermore, cancer cell lines have been shown to require SLC1A5 for their survival in vitro. One of SLC1A5's primary substrates is the immunomodulatory amino acid glutamine, which plays an important role in multiple key processes, such as energy supply, macromolecular synthesis, nucleotide biosynthesis, redox homeostasis, and resistance against oxidative stress. These processes are also essential to immune cells, including neutrophils, macrophages, B and T lymphocytes. We show here that mice with a stop codon in Slc1a5 have reduced glutamine uptake in activated lymphocytes and primary fibroblasts. B and T cell populations and maturation in resting mice were not affected by absence of SLC1A5. Antibody production in resting and immunized mice and the germinal center response to immunization were also found to be normal. SLC1A5 has been recently described as a novel target for the treatment of a variety of cancers, and our results indicate that inhibition of SLC1A5 in cancer therapy may be tolerated well by the immune system of cancer patients.Öğe ATP11C Facilitates Phospholipid Translocation across the Plasma Membrane of All Leukocytes(Public Library Science, 2016) Yabas, Mehmet; Jing, Weidong; Shafik, Sarah; Broeer, Stefan; Enders, AnselmOrganization of the plasma membrane into specialized substructures in different blood lineages facilitates important biological functions including proper localization of receptors at the plasma membrane as well as the initiation of crucial intracellular signaling cascades. The eukaryotic plasma membrane is a lipid bilayer that consists of asymmetrically distributed phospholipids. This asymmetry is actively maintained by membrane-embedded lipid transporters, but there is only limited data available about the molecular identity of the predominantly active transporters and their substrate specificity in different leukocyte subsets. We demonstrate here that the P4-type ATPase ATP11C mediates significant flippase activity in all murine leukocyte subsets. Loss of ATP11C resulted in a defective internalization of phosphatidylserine (PS) and phosphatidylethanolamine (PE) in comparison to control cells. The diminished flippase activity caused increased PS exposure on 7-aminoactinomycin D- (7-AAD(-)) viable pro-B cells freshly isolated from the bone marrow of ATP11C-deficient mice, which was corrected upon a 2-hour resting period in vitro. Despite the impaired flippase activity in all immune cell subsets, the only other blood cell type with an accumulation of PS on the surface were viable 7-AAD(-) developing T cells but this did not result in any discernable effect on their development in the thymus. These findings show that all leukocyte lineages exhibit flippase activity, and identify ATP11C as an aminophospholipid translocase in immune cells.Öğe ATP11C promotes the differentiation of pre-B cells into immature B cells but does not affect their IL-7-dependent proliferation(Springer, 2023) Yabas, Mehmet; Bostanci, Ayten; Aral, SedaThe P4-type ATPases are believed to function as flippases that contribute to the organization of the asymmetric aminophospholipid distribution on the plasma membranes of eukaryotes by their ability to internalize specific phospholipids from the outer leaflet to the inner leaflet. Despite the existence of 14 members of the P4-type ATPases in humans and 15 in mice, their roles in the immune system have not been fully understood. So far, ATP11C was shown to be important for B cells, and mice deficient for ATP11C had a developmental arrest at the pro-B to pre-B cell transition stage of B cell development. Using an ATP11C-deficient pre-B cell line generated through CRISPR/Cas9 engineering, we here tested the role of ATP11C in pre-B cells in vitro and showed that ablation of ATP11C in pre-B cells causes a defect in the flippase activity. We further demonstrated that loss of ATP11C does not impede the proliferation of pre-B cells in response to IL-7. However, pre-B cells lacking ATP11C failed to differentiate into immature B cells upon removal of IL-7. These results suggest that disruption of lipid asymmetry by loss of ATP11C in pre-B cells may control the switch from proliferation to differentiation in pre-B cells.Öğe IgD attenuates the IgM-induced anergy response in transitional and mature B cells(Nature Publishing Group, 2016) Sabouri, Zahra; Perotti, Samuel; Spierings, Emily; Humburg, Peter; Yabas, Mehmet; Bergmann, Hannes; Horikawa, KeisukeSelf-tolerance by clonal anergy of B cells is marked by an increase in IgD and decrease in IgM antigen receptor surface expression, yet the function of IgD on anergic cells is obscure. Here we define the RNA landscape of the in vivo anergy response, comprising 220 induced sequences including a core set of 97. Failure to co-express IgD with IgM decreases overall expression of receptors for self-antigen, but paradoxically increases the core anergy response, exemplified by increased Sdc1 encoding the cell surface marker syndecan-1. IgD expressed on its own is nevertheless competent to induce calcium signalling and the core anergy mRNA response. Syndecan-1 induction correlates with reduction of surface IgM and is exaggerated without surface IgD in many transitional and mature B cells. These results show that IgD attenuates the response to self-antigen in anergic cells and promotes their accumulation. In this way, IgD minimizes tolerance-induced holes in the pre-immune antibody repertoire.Öğe LFM-A13, a potent inhibitor of polo-like kinase, inhibits breast carcinogenesis by suppressing proliferation activity and inducing apoptosis in breast tumors of mice(Springer, 2018) Sahin, Kazim; Tuzcu, Mehmet; Yabas, Mehmet; Orhan, Cemal; Sahin, Nurhan; Ozercan, Ibrahim H.The goals of the present study were to define the anticancer activity of LFM-A13 (alpha-cyano-beta-hydroxy-beta-methyl-N-(2,5-dibromophenyl)-propenamide), a potent inhibitor of Polo-like kinase (PLK), in a mouse mammary cancer model induced by 7,12-dimethylbenz(a)anthracene (DMBA) in vivo and explore its anticancer mechanism(s). We also examined whether the inhibition of PLK by LFM-A13 would improve the efficiency of paclitaxel in breast cancer growth in vivo. To do this, female BALB/c mice received 1 mg of DMBA once a week for 6 weeks with oral gavage. LFM-A13 (50 mg/kg body weight) was administered intraperitoneally with DMBA administration and continued for 25 weeks. We found that LFM-A13, paclitaxel, and their combination have a significant effect on the DMBA-induced breast tumor incidence, mean tumor numbers, average tumor weight, and size. At the molecular level, the administration of LFM-A13 hindered mammary gland carcinoma development by regulating the expression of PLK1, cell cycle-regulating proteins cyclin D1, cyclin dependent kinase-4 (CDK-4), and the CDK inhibitor, p21. Moreover, LFM-A 13 treatment upregulated the levels of I kappa B, the pro-apoptotic proteins Bax, and caspase-3, and down-regulated p53 and the antiapoptotic protein Bcl-2 in mammary tumors. The combination of LFM-A13 with paclitaxel was found to be more effective compared with either agent alone. Collectively, these results suggest that LFM-A13 has an anti-proliferative activity against breast cancer in vivo and that LFM-A13 and paclitaxel combination could be a strategy for the treatment of breast cancer.Öğe Loss of hnRNPLL-dependent splicing of Ptprc has no impact on B-cell development, activation and terminal differentiation into antibody-secreting cells(Wiley, 2021) Yabas, Mehmet; Yazicioglu, Yavuz F.; Hoyne, Gerard F.; Goodnow, Christopher C.; Enders, AnselmThe RNA-binding protein heterogeneous nuclear ribonucleoprotein L-like (hnRNPLL) controls alternative splicing of protein tyrosine phosphatase receptor type C (Ptprc) which encodes CD45. hnRNPLL deficiency leads to a failure in silencing Ptprc exons 4-6 causing aberrant expression of the corresponding CD45 isoforms, namely, CD45RA, RB and RC. While an N-ethyl-N-nitrosourea-induced point mutation in murine Hnrnpll results in loss of peripheral naive T cells, its role in B-cell biology remains unclear. Here, we demonstrate that B-cell development in the bone marrow of Hnrnpll(thu/thu) mice is normal and the number of mature B-cell subsets in the spleen and peritoneal cavity is comparable to control littermates. In response to in vivo immunization, Hnrnpll(thu/thu) mice were deficient in generating germinal center (GC) B cells, and analysis of mixed bone marrow chimeras revealed that the GC B-cell deficiency was a B-cell extrinsic effect of the hnRNPLL mutation. Mature Hnrnpll(thu/thu) B cells proliferated normally in response to various B-cell receptor- and Toll-like receptor-mediated stimuli. Similarly, in vitro stimulation of mutant B cells led to normal generation of plasmablasts, but mutant plasmablasts failed to downregulate B220 expression because of the inability of cells to undergo proper CD45 pre-messenger RNA alternative splicing. These findings collectively suggest that, like in T and natural killer T cells, the mutation disrupts hnRNPLL-mediated alternative splicing of the Ptprc gene in plasmablasts, but this dysregulation of Ptprc alternative splicing does not affect the development and function of B cells.Öğe A Next Generation Formulation of Curcumin Ameliorates Experimentally Induced Osteoarthritis in Rats via Regulation of Inflammatory Mediators(Frontiers Media Sa, 2021) Yabas, Mehmet; Orhan, Cemal; Er, Besir; Tuzcu, Mehmet; Durmus, Ali Said; Ozercan, Ibrahim Hanifi; Sahin, NurhanOsteoarthritis (OA) is a chronic and debilitating disease of the knee joint. OA of the knee is initiated by physical damage and accumulated oxidative stress, followed by an exaggerated inflammation leading to cartilage damage. Currently, no effective and safe therapeutic option capable of restoring articular cartilage tissue and joint architecture is available. We here report a novel and highly bioavailable formulation of curcumin, labeled as Next Generation Ultrasol Curcumin (NGUC), which was 64.7 times more bioavailable than natural 95% curcumin extract as demonstrated in rat bioavailability studies. We further investigated the protective effect of NGUC against monosodium iodoacetate (MIA)-induced knee OA in rats. Analysis of X-ray and histopathological images revealed that NGUC supplementation restored joint architecture and reduced swelling of joints induced by MIA. NGUC treatment caused a significant reduction in the levels of inflammatory mediators such as TNF-alpha, IL-1 beta, IL-6, COMP, and CRP, and expressions of MMP-3, 5-LOX, COX-2, and NF kappa B in synovial tissue of rats with MIA-induced OA. NGUC also decreased serum MDA level and increased the levels of antioxidant enzymes SOD, CAT, and GPX. Thus, our results indicate that a novel formulation of curcumin with enhanced bioavailability effectively ameliorates the pathophysiology of OA.Öğe Prevention of DMBA-induced mammary gland tumors in mice by a dual-function inhibitor of JAK3 and EGF receptor tyrosine kinases(Taylor & Francis Ltd, 2020) Sahin, Kazim; Yabas, Mehmet; Orhan, Cemal; Tuzcu, Mehmet; Sahin, Taha K.; Ozercan, Ibrahim H.; Qazi, SanjiveObjectives: We tested the chemopreventive effect of WHI-P131 in side by side evaluation with the standard anti-breast cancer drug paclitaxel in the well-established 7,12-dimethylbenz(a)anthracene (DMBA)-induced breast cancer model. Methods: One hundred BALB/cmice were divided into five groups. (i) Control (ii) DMBA (iii) DMBA+ Paclitaxel (10 mg/kg) (iv) DMBA+WHI-P131 (Janex1, 50 mg/kg of BW, i.p, three times per week) (J) (v) DMBA+P+J. The duration of study was 25 weeks. Results: Our findings demonstrate that WHI-P131 impedes DMBA-induced carcinogenesis, reduces size, weight, and load of tumors (P < 0.001) in DMBA-challenged mice and improves their survival outcome (P < 0.01). The tumors developing despite WHI-P131 chemoprevention displayedattenuated levels of JAK3, STAT3, and NF-kappa B as well as increased I-kappa B expression (P < 0.001). Notably, these tumors exhibited significantly decreased levels of phosphorylated AKT-PI3-Kinase pathway signaling proteins p-mTOR, p-p70S6K1, and p-4E-BP1 (P < 0.001). Our findings are consistent with a model in which DMBA-induced malignant clones with low-level expression of the six signature proteins JAK3/STAT3/NF-kappa B/p-mTOR, p-p70S6K1/p-4E-BP1, albeit not as aggressive as their JAK3/STAT3/NF-kappa B overexpressing counterparts are capable of escaping chemo-preventive effects of WHI-P131. Conclusion: These insights may provide the foundation for new chemo-preventive strategies in which WHI-P131 is applied to prevent the development of aggressive forms of breast cancer.Öğe The Role of Alternative Splicing in the Control of Immune Homeostasis and Cellular Differentiation(Mdpi, 2016) Yabas, Mehmet; Elliott, Hannah; Hoyne, Gerard F.Alternative splicing of pre-mRNA helps to enhance the genetic diversity within mammalian cells by increasing the number of protein isoforms that can be generated from one gene product. This provides a great deal of flexibility to the host cell to alter protein function, but when dysregulation in splicing occurs this can have important impact on health and disease. Alternative splicing is widely used in the mammalian immune system to control the development and function of antigen specific lymphocytes. In this review we will examine the splicing of pre-mRNAs yielding key proteins in the immune system that regulate apoptosis, lymphocyte differentiation, activation and homeostasis, and discuss how defects in splicing can contribute to diseases. We will describe how disruption to trans-acting factors, such as heterogeneous nuclear ribonucleoproteins (hnRNPs), can impact on cell survival and differentiation in the immune system.
